Effect of intrauterine growth retardation on developmental changes in DNA and [14C]thymidine metabolism in different regions of rat brain: histological and biochemical correlations

Intrauterine growth retardation was induced in the rat by clamping the uterine artery on day 17 of gestation. The effect of hypotrophy on DNA synthesis was studied in two different cerebral structures: hippocampus and cerebellum. Accumulation of DNA in these structures was biochemically measured in parallel to the incorporation of methyl-[14C]thymidine into nucleic acid at different ages and correlated with autoradiography. The various metabolites of thymidine in acid-soluble fraction were determined by using chromatographic procedures. Phosphorylation defects or reduced utilization of thymidine were found in hypotrophic rats and may delay the DNA synthesis. An essay of catch-up occurred with a different timing according to the cerebral region studied. A morphological and DNA synthesis. An essay of catch-up occurred with a different timing according to the cerebral region studied. A morphological and autoradiographic study after incorporation of [3H]thymidine was carried out in parallel. The neuronal and glial components of cytogenesis were analyzed separately and a good correlation was observed between histological and biochemical data in both groups of animals.

In vivo voltammetric measurement of extracellular 5-hydroxyindoleacetic acid in the denervated striatum after transplantation of mesencephalic raphe neurons

In vivo differential pulse voltammetry with carbon fiber electrodes was used to monitor extracellular 5-hydroxyindoleacetic acid (5-HIAA) levels in a serotonergic denervated target area, the striatum, before and after transplantation of mesencephalic raphé nuclei into the lateral ventricle in the rat. The amplitude of the electrochemical signal recorded in the striatum on the transplanted side was found to be comparable to that measured in control striatum whereas the signal measured from the contralateral nontransplanted striatum was negligible. These findings suggest that mesencephalic raphé nuclei transplants establish connections with the host tissue.

Adult age destruction versus neonatal age destruction of the serotonin system: two models to investigate the survival of serotonin neurons transplanted in adult rats

Mesencephalic raphe nuclei were transplanted via the cisterna magna in the IVth ventricle of adult rats having received either a neonatal or an adult age destruction of the serotonin system. In neonatally treated rats both serotonin (5-HT) and glial fibrillary acidic protein (GFA) immunocytochemistry showed an absence of survival of 5-HT neurons in the transplants. However, many 5-HT immunoreactive cell bodies and processes were detected in 10-month-old transplants in adult treated animals. These results suggest that recognition processes between the target tissue and the implant may be a prerequisite for the survival of grafted neurons.

Cells with neuronal properties in permanent cultures of quail embryo neuroretinas infected with Rous sarcoma virus

Neuroretina cells from 7-day quail embryos infected 'in vitro' with the mutant ts NY-68 of Rous sarcoma virus, were established into permanent cultures. An initial stage of cellular proliferation was followed by a period of minimal multiplication. After recovery from this crisis, cell proliferation resumed. About 30% of the cells had binding sites for tetanus toxin and the monoclonal antibody A2B5 which seem to be specific for neurons, and an ultrastructural study suggested the presence of neurons and Müller (astroglial) cells. The specific activity of glutamic acid decarboxylase, the enzyme responsible for the synthesis of the neurotransmitter gamma-aminobutyric acid was high (10-30 nmol CO2/h/mg of protein) and electrophysiology showed that some cells had 'active' membranes. After about 18 months in culture, approximately 20% of the cells were able to respond to electrical stimulation by producing action potentials which were inhibited by 10(-7) M tetrodotoxin. These electrophysiological properties are stable: they have been repeatedly found at regular intervals throughout a 20 months period. Furthermore, a clone in which all tested cells are excitable, has been derived from the mass culture. Quail embryo neuroretina cells with typical neuronal properties can thus be established into permanent cultures after infection with Rous sarcoma virus.

Multiplication and differentiation of glial cells in the optic nerve of the postnatal rat. A reassessment

In order to establish a firm basis for our studies on cell reactivity during Wallerian degeneration in the optic nerve of the rat, gliogenesis in this fiber tract was reassessed. Rats aged 2, 5, 8 and 20 days (key-stages) received a single injection of tritiated thymidine and were sacrificed after a survival period of 1, 3, 5, 10 and 20 days. Before the 5th postnatal day, glioblasts and astrocytes are the only cell types identifiable in the optic nerve. Most of astrocytes undergo their last mitosis during this period. Oligodendrocytes are first seen after the 5th postnatal day, and their maturation proceeds through a regular sequence of light, medium and dark cells. Detailed analysis of this time-course reveals that those precursors of oligodendrocytes that undergo last mitosis at the 5th postnatal day are retarded in their differentiation as compared with those undergoing their last mitosis during the 6-8 days period. When considering glio-axonal interactions, the onset of oligodendrocyte differentiation could proceed in two phases, especially at the 5 day key-stage, with an initial signal triggering the cessation of mitosis of glioblasts and a second signal inducing their maturation, conditioned by the type of surrounding tissue.

Identification of cDNA clones coding for rat tyrosine hydroxylase antigen

Five recombinant DNA plasmids have been constructed that contain structural gene sequences for rat tyrosine hydroxylase [TyrOHase; tyrosine 3-monooxygenase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2]. Rat pheochromocytoma PC 12 cell line, which contains relatively high levels of catecholamine-synthesizing enzymes, was used to purify RNA. TyrOHase cDNA clones were identified by screening 350 cDNA clones constructed from partially purified TyrOHase mRNA. A rapid and powerful screening of the recombinant clones by differential colony hybridization was possible because TyrOHase is a tissue-specific protein. The final selection relied on the ability of cDNA inserts to hybridize specifically to TyrOHase mRNA as judged by cell-free translation and immunoprecipitation. Blot hybridization analysis of polyadenylylated RNA from PC 12 cells indicated a major mRNA species of 1.9 kilobases. A species of the same size was identified from a human pheochromocytoma tumor, indicating a crossreactivity between rat TyrOHase cDNA and human TyrOHase mRNA.

Subgranular zone of the dentate gyrus of young rabbits as a secondary matrix. A high-resolution autoradiographic study

Cell genesis in the subgranular zone of the dentate gyrus of 2-month-old rabbits has been investigated. After incorporation of tritiated thymidine, electron microscopic autoradiography allowed description of the ultrastructure of the cells labelled and the progressive transformation of these cells into granular neurons to be followed. Quantitative evaluation of the time course of this transformation has been performed by light microscope autoradiography using 1-micrometer sections. Precursor cells, labelled initially with 3H-thymidine, were transformed after 5 days into early neuroblasts, these cells in turn giving rise to neurons some 8 days later. At the latest time period examined (42 days), 80% of the labelled cells were neurons; more than 10% remained as precursor cells. It is suspected that the latter may behave as reserve cells. Small numbers of glial cells, astrocytes, and microglia, scattered throughout the hilus of the dentate gyrus and the molecular layer, were found labelled, and it is possible that they arise from a different precusor pool. It is concluded that the subgranular zone functions as a secondary matrix for granule neurons of the dentate gyrus in young rabbits. These late-forming and apparently synaptically uncommitted neurons may be recruited during the development and refinement of postnatal behavioral substrates, by one or other of the dominant afferent systems.

Radioautographic evidence for the protracted proliferation of glial cells in the central nervous system of jimpy mice

Proliferation of glial cells has been studied in the central nervous system of jimpy mice and control littermates with [3H]thymidine radioautography. It was found that the proliferation of glial precursors was protracted in the 3 regions studied: spinal cord, cerebellum and corpus callosum. The difference between jimpy and littermates became obvious in each of these regions at the onset of myelination. It is concluded that the maturation of the oligodendrocyte is the target of the mutation. The protracted proliferation of glioblasts is a consequence of the absence of stable interactions with the axons.

[In vitro synthesis of tyrosine hydroxylase]

RNA from PC 12 cells was translated in a cell-free system and the peptides synthesized in vitro were analyzed by immunoprecipitation with an anti-T.H. serum raised in Rabbit. Analysis of the immunoprecipitate on a SDS-polyacrylamide gel reveals a major band with a molecular weight of 62000 dalton. A protein of the same molecular weight was also precipitated from a PC12 cell lysate. This molecular weight of 62000 dalton corresponds to the reported for tyrosine hydroxylase purified from PC12 cells.

Proliferation of neuroglial cell lines in the degenerating optic nerve of young rats. A radioautographic study

Wallerian degeneration was investigated in the rat optic nerve after eye enucleation at 2, 5, 8, and 20 D.P.N. (key stages), corresponding to the periods of premyelination, myelination, and postmyelination. The incorporation of tritiated thymidine, and subsequent radioautography of semithin sections, allowed the identification and enumeration of labeled cells, and the computation of labeling indices of the different cell types (glioblasts, astrocytes, oligodendrocytes, and microglia) in the operated as well as the contralateral nerve. The comparison of labeling indices and absolute numbers of labeled cells in each category suggests an increased transformation of glioblasts into astrocytes, and absence of differentiation and stabilization of oligodendrocytes due to the failure of the axonal signal, and a transformation of pericytes into interstitial microglia. The first three key stages (2, 5, and 8 D.P.N.) are characterized by the integration of reactive gliosis and more or less marked failure of myelination gliosis, whereas the last one (20 D.P.N.) shows essentially a reactive gliosis. The modifications of the neural environment interfere with the genetic program of gliogenesis, illustrating the postnatal plasticity of the central nervous system.

[Evidence of autapses in vitro by electron microscopy combined with iontophoretic intracellular injection of peroxidase]

The existence of autapses, i. e. of synapses between a neuron and its own axon, is demonstrated in vitro by means of Horseradish peroxidase (HRP) iontophoretic filling, combined with electron-microscopic (EM) analysis. After the injection of one single Purkinje cell per explant (Kitten cerebellum), the ultrastructural observation (serial thin sections) reveals the presence of both pre- and post-synaptic labelled structures. Axodendritic autapses are thus illustrated and their significance is discussed in view of earlier morphological and electrophysiological data.

In vitro differentiation of hypothalamic magnocellular neurons of guinea pigs

The development of neurophysin-oxytocin and neurophysin-vasopressin containing neurons of the guinea pig was studied in vitro. Supraoptic (SO) and paraventricular (PV) nuclei were explanted from guinea pig foetuses at the 40th day of gestation and cultured in Maximov slides for nearly fifty days. The cultures were observed daily under a phase-contrast microscope. Explants were fixed every five days for observation with the electron microscope. At the time of explantation, magnocellular neurons were still immature. They acquired the morphologic characteristics of mature neurons, with axosomatic synapses, after about 10 days in vitro. After 15-20 days in vitro, they contained in addition neurosecretory granules (NSG), first in the Golgi region, then also dispersed in the cytoplasm. In the oldest culture (45-50 days), signs of granulolysis were regularly found. It appears that magnocellular neurosecretory neurons are able to differentiate in vitro from a primitive state in the absence of specific stimulation.

Differential radiosensitivity of neurons and neuroglia of the hippocampus in the adult rabbit

Adult rabbits were subjected to 4.5 Gy of whole-blody or brain alone gamma-irradiation, and their hippocampus was examined with the light and electron microscope. Pycnotic cells were found at the base of the granular layer of the dentate gyrus in the so-called subgranular zone, as soon as 3 h after irradiation, and were cleared up by active phagocytosis after 48 h. Some of these cells appeared as undifferentiated, whereas others were differentiating granule cells, and possibly immature neuroglia. The extent of cell necrosis was contingent upon the age of the animal, the oldest animal studied (27 months) showing only sparse lesion of that type. Astrocytes and microglia were responsible for the phagocytosis of dead cells. Another type of lesion was found in the nuclei of the mature granule cells and consisted of light spots which appeared 1 h after the irradiation and disappeared almost completely after 48 h. Pyramidal cells did not show any of these two lesions. It is concluded that the laterations in the electrical activity of pyrimidal cells, following irradiation, are at least partly due to lesions affecting the dentate gyrus. Radionecrosis in the subgranular zone is related to the presence of immature cells in this region.

Absence of the major dense line in myelin of the mutant mouse "shiverer"

The myelin of the central nervous system (CNS) of the mutant mouse Shiverer is characterized by the absence of the major dense line (MDL). The intraperiod line, as seen in conventional electron micrographs and in freeze-fractured replicas, appears normal. Peripheral myelin, as seen in ventral and dorsal roots of spinal cord, is unaffected by the mutation. During the period of active myelination, the cytoplasm of most oligodendrocytes (ODs) is packed with electron-lucent vacuoles in continuity with the Golgi apparatus and with bundles of microtubules. It is concluded that a metabolic pathway possibly involving the Golgi apparatus, and contributing to the formation of the MDL is selectively affected in this mutant.

Immunochemical studies of myelin basic protein in shiverer mouse devoid of major dense line of myelin

The myelin-deficient mutant Shiverer (Shi/Shi) lacks basic protein (MBP) in the myelin of its central nervous system (CNS). Less than 3% of the normal content in MBP is present in a brain extract of Shi/Shi as determined by radioimmunoassay. Indirect immunofluorescence is negative when using specific anti-MBP serum. The importance of Shi/Shi (as compared to other hypomelinating mutants) stems from the specificity of this genetic lesion, i.e. the lack of basic protein.

Jimpy mouse myelin revisited with freeze-fracture

Corpus callosum, cerebellum, and spinal cord from Jimpy mice, and control littermates, 15 and 21 days old, were prepared for freeze-fracture in a "cryofract" apparatus. The few myelinated axons in the Jimpy exhibited a striking paucity of particles in myelin P faces, though tight junctions were present. In addition, small maculae of particles were found on these P faces. Peripheral myelin appeared normal, both for the quantity and disposition of particles on their P faces.

Dendro-dendritic pentalaminar junctions in the Weaver mouse cerebellum

The cerebellum of weaver mouse is characterized by an extensive reorganization of cell interaction secondary to the absence of mature granule cells. One yet undescribed modality of reorganization found in the hemispheres of 1-month-old animals consisted in the presence of dendro-dendritic pentalaminar junctions. The possible formation of these junctions by fusion of facing post-synaptic densities is discussed.

Differentiation of chick embryo neuroretina cells in monolayer cultures. An ultrastructural study. I. Seven-day retina

Neuroretinas from 6--7 day-old chick embryos were cultivated after trypsin dissociation as monolayer cultures in Petri dishes, and examined after various intervals of time with the electron microscope. Soon after plating, cells begin to reaggregate in small clumps, and typical rosettes are formed. During the first week in vitro, cells appear to differentiate as neuroblasts and presumed Müller cells; the latter form a continous sheet on the substrate, upon which neuroblasts migrate and grow their neurites. Differentiated ribbon synapses are found after 8 days in vitro, the time at which they normally appear in situ. After 15 and 21 days in vitro, synapses are still found in large numbers, mimicking their "in vivo" counterparts. Photoreceptor cells were identified on the basis of the presence of typical ribbons in their cytoplasm, but no outer segment was found. It appears then that synaptogenesis in the retina is programmed independently of the tissue environment, which is markedly disturbed in the monolayer culture.